1. Technical Field
The present invention relates generally to an apparatus for monitoring optical signal performance in a wavelength division multiplexing system, and in particular, to an apparatus for monitoring optical signal performance in a link section without a fiber amplifier.
2. Related Art
A wavelength division multiplexing (WDM) optical communication system measures wavelength, optical power, and optical signal to noise ratio (OSNR) of an optical signal being transmitted through an optical transmission line on an optical link in order to monitor the performance of the optical signal itself. Also, the WDM optical communication system is equipped with a device for detecting optical signal degradation in a particular link, and sending a notification of the optical signal degradation to a system operator and a manager or providing information that enables restoration of the degradation by itself.
In general, the WDM optical communication system for use in the measurement of the optical wavelength, optical power, and optical signal to noise ratio of the wavelength division multiplexed optical signal includes an optical spectrum analyzer mounted with a diffraction grating and a photo diode array, a fiber bragg grating (FBG), and a photo diode array. However, when optical equipment like the diffraction grating and the photo diode array are employed, it is difficult to achieve a more efficient optical space array. In fact, this problem is not entirely new to anyone skilled in the art who is well aware of the difficulty with the precise measurement of the optical wavelength, the optical power, and the optical signal to noise ratio especially when the optical space array has not been done accurately.
As an attempt to solve the problem, there is a different type of equipment for measuring the optical signal, the optical power and the optical signal to noise ratio of the WDM optical system disclosed in Korean Pat. No. 10-292809 entitled APPARATUS FOR MEASURING THE WAVELENGTH, OPTICAL POWER AND OPTICAL SIGNAL-TO-NOISE RATION OF EACH OPTICAL SIGNAL IN WAVELENGTH-DIVISION MULTIPLEXING OPTICAL COMMUNICATION, invented by Lee et al., with patent registration date 27 Mar. 2001, corresponding to U.S. Pat. No. 6,396,574 issued on 28 May 2002. According to the disclosure, a fiber amplifier is employed to measure the wavelength division multiplexed optical signal that is transmitted over the optical link. For example, the equipment uses an amplified spontaneous emission (ASE) that is generated by amplifying the wavelength division multiplexed optical signal in an Erbium doped fiber amplifier. In addition, the equipment includes two fiber bragg gratings (FBG) for measuring a specific wavelength of the amplified spontaneous emission outputted from the fiber amplifier, and generates a reference wavelength for measuring the wavelength division multiplexed optical signal. Despite such a configuration, the equipment could not be used for the WDM system without a fiber amplifier. Besides, when the measurement is obtained using the equipment, that is, when two optical signals reflected from two FBG are used as the reference wavelength of the amplified spontaneous emission, the resolution of the measurement is low.
Efforts have been made to improve optical signal monitoring. Exemplars of recent efforts in the art include U.S. Pat. No. 5,796,479 to Derickson et al., entitled SIGNAL MONITORING APPARATUS FOR WAVELENGTH DIVISION MULTIPLEXED OPTICAL TELECOMMUNICATIONNETWORKS, issued on Aug. 18, 1998, U.S. Pat. No. 5,969,834 to Farber et al., entitled METHOD AND APPARATUS FOR MONITORING WAVELENGTH MULTIPLEXED OPTICAL SIGNALS, issued on Oct. 19, 1999, U.S. Pat. No. 6,268,943 to Kang, entitled OPTICAL SNR MEASURER IN WDM OPTICAL TRANSMITTING DEVICE, issued on Jul. 31, 2001, and an article authored by Kang et al., published in October 1998 in IEEE Photonics Technology Letters, and entitled TEMPERATURE-INDEPENDENT STRAIN SENSOR SYSTEM USING A TILTED FIBER BRAGG GRATING DEMODULATOR.
While these recent efforts provide advantages, it is noted that they fail to adequately provide an apparatus for efficiently and conveniently monitoring optical signal performance in a wavelength division multiplexing system.